Spoiler alert! The following contains details from Netflix’s true-crime documentary “Lover, Stalker, Killer” (now streaming).

Nancy Raney hadn’t heard her daughter’s voice or seen her bright smile and twinkling hazel eyes in years. Cari Farver all but vanished in November 2012, abandoning her teenage son Max in his grandmother's care. Farver supposedly only surfaced to harass, threaten and stalk her brief flame, Dave Kroupa, and his current romantic interest, Shanna "Liz" Golyar.

Farver and Kroupa dated casually for two weeks before he called things off, just before she disappeared. In response, he received rageful messages from Farver’s phone. “I’m going to destroy the things you care about,” one message read. “Your life will be ruined for ruining mine.” The torment, which persisted for years, is chronicled in Netflix’s suspenseful true-crime documentary, “Lover, Stalker, Killer” (now streaming).

Farver purportedly broke into the homes of Kroupa and Golyar, and spray-painted “Whore” on Golyar's wall. One day Kroupa received a text from Farver informing him that she’d set Golyar’s house ablaze. Golyar’s kids weren’t home, but her pets perished in the fire.

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The puzzling case caught the attention of James “Jim” Doty, a Sergeant Investigator with the Pottawattamie County Sheriff's Office in Council Bluffs, Iowa, and his colleague, Deputy Ryan Avis.

“Me and Ryan went and requested to look at this case,” Doty says in an interview, “because it struck us as odd that this single mom had just vanished and left her son behind.”

Doty and Avis wanted to start from square one for their investigation and explore all possibilities.

“You've probably seen this on other shows that cops get tunnel vision, and I think the investigators at the beginning of this had a little tunnel vision,” Doty says. “They just bought into ‘Cari’s off her meds' type of thing. (Farver had been diagnosed with bipolar disorder and didn’t have her medication with her.) But we wanted to avoid that.”

So Avis looked for evidence that Farver was alive. He searched for activity on her bank account and people who might’ve seen her. Doty proceeded as if Farver had died, “because nobody had seen her for years.”

In a surprising twist, they traced all the digital communications to Golyar, who murdered Farver in 2012 and had been impersonating her ever since. Authorities arrested Golyar in 2016 and charged her with first-degree murder and second-degree arson. She was convicted on both counts in 2017 and sentenced to life without the possibility of parole.

In addition to talking about what is shown in the documentary, Doty also revealed to USA TODAY things viewers won't see.

What 'changed the case' for Doty

Doty says meeting Raney, Farver’s mom, “changed the case for me quite a bit,” intensifying his desire to resolve it. “Before, you're trying to get answers about what happened to a lady named Cari, (but) you don't really know who Cari is,” Doty says. “But once you really get to know her mom and see how much her mom cares, her mom becomes basically a living victim for you that's had to go through all this harassment and her daughter's name getting (dragged) through the mud for years.”

In the film, Raney says she cried when Doty suspected foul play in Farver’s disappearance, “because nobody with authority had ever told me that.”

Liz Golyar exuded ‘not one bit of remorse’

Doty says in his interactions with Golyar she betrayed no nervousness — even while being interrogated — or regret over killing Farver and what she put Kroupa through.

“This is the level of cold-heartedness,” Doty says, recalling how Golyar messaged Farver’s family from her Facebook account. Hoping to verify his mom’s identity, Farver’s son Max sends a few questions to his mom's Facebook, inquiring about things only she would know, like the name of their family’s first dog.

“Obviously he gets no response from Liz because she doesn't know the answer to any of those,” Doty says. “So Max at that point knows, ‘All right, this definitely isn't my mom. It's somebody else posing as her.’”

But time passes, and Max — now a high-school senior longing for his mom to witness his milestone — reaches out once more. He writes “‘Hey, Mom, if that's really you, please show up to my graduation,’” Doty says. “I don't know how that doesn't break anybody's heart, but it didn't affect (Liz) one bit. She didn't care that she was hurting Cari’s mom, her child or anything. Not one bit of remorse.”

Anthony ‘Tony’ Kava committed on a ‘different level’ to the case

Doty says everyone worked tirelessly on the investigation, but says Special Deputy Anthony "Tony" Kava, Digital Forensics Investigator, “worked at a different level of hard. He probably put in more hours on this than maybe all of us combined.” Kava was instrumental in proving Golyar was the source of the electronic threats and helped prosecute her, Doty says. In a moving moment from the documentary, Kava shares that he put off having surgery on a growing brain tumor because it would’ve impaired his ability to work on the case.

“When it came to testifying, I just got up on the stand and was asked questions,” says Doty. But Kava “put together about a 1,000-slide presentation that was used as a piece of evidence to explain all of the digital aspects of this case. Without that, how do you prove that it's Liz doing all this without something so demonstrative that it's able to just blow away the judge: ‘OK, there's no shadow of a doubt (that) Liz is behind this.’”

At the end of the documentary, Nancy says she will always be grateful to Doty, Kava and Avis, explaining ,“They saved my sanity, and they’ll always be my boys.”

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